(1) Field of the Invention
The present invention relates to digital broadcast reception technology for receiving a repeatedly-transmitted broadcast wave that includes “interactive data”, and for achieving pseudo-interactive communications.
(2) Description of the Prior Art
In recent years, fee-based television (TV) programs have been broadcasted.
Japanese Laid-Open Patent Application No. 11-243535 discloses a digital communication satellite broadcast service. For this communication satellite broadcast service, a plurality of transport streams (hereafter called “TS”) for digital data are broadcasted in parallel. The number of transport streams broadcasted in parallel is equal to a number of transponders. A plurality of transport packets (hereafter “TP”), which contain data corresponding to a plurality of programs, are time-division multiplexed into each TS. A user selects a given program contained in a TS, and watches the program.
With a fee-based digital broadcast, a viewing of a program is restricted to predetermined viewers. To restrict viewers, the following method is used.
Encryption (hereafter, “scrambling”) is performed separately for each TP (hereafter, “AV (audio-video) TP”) containing video data and audio data for programs. A descrambling key to descramble such scrambled AV TP, and program attribute information for the programs make up program information (hereafter, “ECM”) and are contained in another TP (hereafter, “ECM TP”). Such ECM TP and AV TP are broadcasted together. This ECM TP is also scrambled. A work key to descramble the scrambled ECM TP, and subscription information make up individual information (hereafter, “EMM”) and are stored in an integrated circuit (IC) card, which is inserted into each receiving device. The scrambled ECM TP is first descrambled with the work key on the IC card, and the descrambling key is extracted from the descrambled ECM TP. After this, the program attribute information in the ECM and the subscription information, which is given to each user on an IC card, are compared to specify a program that can be descrambled. The specified program is then descrambled using the extracted descrambling key, and images and sounds for the program are presented to the user.
Such fee-based broadcast service usually allows users to watch a fee-based program at no charge for a predetermined time (hereafter a “preview time”).
Digitalization of a broadcast makes it possible to broadcast a great amount of digital data information other than video and audio data. Such digital data information broadcast is now available in a digital satellite broadcast service. In this digital satellite broadcast service, digital data information is broadcasted with video data and the like in only one direction from a sending station, and therefore there is no interactive process with receiving terminals in this transmission.
Japanese Laid-Open Patent Application No. 10-313449 discloses one example of such broadcasting. According to this patent application, a sending station repeatedly broadcasts a plurality of sets of digital data information, and a receiving terminal receives one of the plurality of sets of digital data information while switching from one set of data information to another to simulate interactive communication with the sending station. In this specification, digital data information broadcasted in this manner is called “interactive data”.
Broadcasting such interactive data, however, involves the following problems.
First, as there is no restrictions in viewing such interactive data during the aforementioned preview time, a viewer can view all the interactive data broadcasted with a previewed program, using a receiving terminal or the like during the preview time if the interactive data is not updated during a broadcast of the previewed program.
Secondly, interactive data is accumulated in memory of a receiving terminal, unlike video data and audio data. This allows a user freely to present interactive data, using the accumulated interactive data even after the preview time has expired. This is not desirable for a broadcast provider.